I know the basics of the French colonial situation there, but I'd like to know the specifics behind the creation of their writing system. Since the Vietnamese script is unique to Vietnam I assume that there was some conscious design behind it. Thanks for any answers!
The relevant Wikipedia article is pretty good.
The modern Viet alphabet is very similar to the original Romanization of Alexandre de Rhodes's great dictionary back in the 17th century.
Alexis Michaud has done a translation of Haudricourt's 1949 paper on some of the peculiarities of the Viet alphabet, you can read it here
It was first formulated by Jesuit missionaries in the 1600s.
The man accredited with its creation was Alexandre de Rhodes who published a dictionary called Lusitanum-Latinum-Annamiticum (Portuguese-Latin-Vietnamese).
It was used in conjunction with Chữ Nôm (Vietnamised Chinese script) until the latter was abolished in the late 1920s, early 30s during French colonial rule.
The script proved to be effecient enough to bring large numbers of people out of illiteracy compared to the old character-based script.